Memoirs of the Academy for 1780, p. 355. and from that Essay the
materials of this chapter are extracted.
If, after having cooled any body to the freezing point, it be exposed in
an atmosphere of 25 (88.25 ), the body will gradually become heated,
from the surface inwards, till at last it acquire the same temperature
with the surrounding air. But, if a piece of ice be placed in the same
situation, the circumstances are quite different; it does not approach
in the smallest degree towards the temperature of the circumambient air,
but remains constantly at Zero (32 ), or the temperature of melting ice,
till the last portion of ice be completely melted.
This phenomenon is readily explained; as, to melt ice, or reduce it to
water, it requires to be combined with a certain portion of caloric;
the whole caloric attracted from the surrounding bodies, is arrested or
fixed at the surface or external layer of ice which it is employed to
dissolve, and combines with it to form water; the next quantity of
caloric combines with the second layer to dissolve it into water, and so
on successively till the whole ice be dissolved or converted into water
by combination with caloric, the very last atom still remaining at its
former temperature, because the caloric has never penetrated so far as
long as any intermediate ice remained to melt.
Upon these principles, if we conceive a hollow sphere of ice at the
temperature of Zero (32 ) placed in an atmosphere 10 (54.5 ), and
containing a substance at any degree of temperature above freezing, it
follows, 1st, That the heat of the external atmosphere cannot penetrate
into the internal hollow of the sphere of ice; 2dly, That the heat of
the body placed in the hollow of the sphere cannot penetrate outwards
beyond it, but will be stopped at the internal surface, and continually
employed to melt successive layers of ice, until the temperature of the
body be reduced to Zero (32 ), by having all its superabundant caloric
above that temperature carried off by the ice. If the whole water,
formed within the sphere of ice during the reduction of the temperature
of the included body to Zero, be carefully collected, the weight of the
water will be exactly proportional to the quantity of caloric lost by
the body in passing from its original temperature to that of melting
ice; for it is evident that a double quantity of caloric would have
melted twice the quantity of ice; hence the quantity of ice melted is a
very exact measure of the quantity of caloric employed to produce that
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